There is actually a large amount of relatively modern* lighting currently being stored in the gardens. It might not be related at all, but I suspect the park did actually buy the lighting for the garden light attractions, so theoretically it would be relatively easy to reintroduce something similar.
* I'm not an AV person, but to my untrained eye it looks like the same sort of lighting used for the Garden Light Trail.
I'd expect the park to have purchased the minimum amount of lighting, fixtures and electronic components to allow for a basic wash of the gardens. Anything more ambient, or themed, anything which changed or was only there for a seasonal event, I'd expect to be rented. Warwick Castle now runs its own light trail at Christmas, designed internally, but all of the lighting and speakers are rented for the duration of the event.
It's far more cost effective, in most instances, to rent kit than buy it. As I'm sure
@Burbs can attest, most venues outside of permanent West End productions, will seldom have their own AV kit (aside from the bare minimum), and will act as blank canvasses for the next incoming show.
Even in film, television and theatre, where you rely on equipment constantly, you tend to rent it for the duration of the production. Each will have its own unique set of circumstances, technology changes and evolves, the demands will be different each time.
A Sony FX9 camera, for the body alone, will cost you £12,474 to buy. You can rent a full Sony FX9 kit, with viewfinders, eye pieces, storage media, lenses, tripod, mics, bells and whistles for around £200 per day (most hire houses will also not charge you for Saturdays and Sundays). The camera will be considered dated in 2-3 years. Renting also ensures that you don't have to worry about the long-term maintenance or storage of the kit. Heck, you can't even buy a Panavision or IMAX camera, you have to rent them from the relevant companies directly.